Field of the Invention
The present invention relates to the field of prevention of post-concussive hearing trauma, and more specifically to physical devices, designed to be worn in the ear canal or affixed to the outer ear to block extreme shock wave damage to the hearing organ.
Brief Description of the Related Art
There is a need for devices that provide protection from blast overpressure as experienced by military personnel on a battlefield. Communication is the single most important asset of our battlefield forces. Combat elements function as a team and must be able to immediately react to unanticipated operational contingencies. Instantaneous and uninterrupted communication is fundamentally important and great effort has been made to insure efficient and redundant communication within and among tactical units in the field. However, a crucial aspect of this communication network has been overlooked—blast induced hearing loss. Frontline troops injured by explosions currently experience 64% hearing loss, and represent an instantaneous reduction in the immediate effective in-theater force, affecting the most critical element in the entire chain—the advance-line soldier.
For over 500 years, national entities have used explosive charges to wage war. Front line medical assets; improvements in surgical techniques and the creation of Shock Surgical Trauma Teams have significantly reduced the mortality radius from explosive impacts. Use of individual protective gear and body armor mitigate dismemberment and secondary limb damage in range of explosives allowing prolonged duration of the effective force on the battlefield. Hearing damage encountered in what we term the otologic disablement zone extending hundreds of meters away from the impact area remains an unaddressed component of battlefield morbidity and tactical incapacitation.
In regional proximity to the target, an explosive charge can produce a high-pressure shock wave with specific physical pressures which not only rupture the eardrum, displacing the middle ear ossicles, but also destroy inner ear sensory cells in the specific frequency ranges most utilized for interpersonnel communication. This acute hearing loss results from sharp impulse rise in sound wave intensity produced by proximity to battlefield explosions. The damage is immediate and irreversible. Soldiers within the otologic disablement zone often do not exhibit any outward sign of hearing impairment just after exposure other than being unable to respond to commands. Battlefield management of the effective force assets become secondarily compromised when the disabled team members are unable to respond to commands. This loss of unit cohesion impedes the attainment of mission objectives. Valuable time is lost as the effective force adapts to this compromised situation.
According to the office of the Army Surgeon General, hearing loss in soldiers sustained to blast injuries are running 64%, by far the highest category of battlefield injuries, resulting in significant reduction in effective force in the current War Against Terrorism. The year 2004 had the highest rate of increase in combat injuries hearing loss since records began to be kept in the mid 20th century, a period that included for example; WWII, the Korean War, The Vietnam Conflict, the Marine deployment in Lebanon, The Gulf War, and OIF/OEF.
In the 2005 survey of hearing protector efficacy, under operational conditions, it was found that all the tested devices attenuated C-weighted peak level to less than 130 dB, well below the sound peaks experienced in explosions encountered in OIF. In practice, these devices attenuated noise by only 10-30 dB.
Proximity to explosion is more important that size. Studies on conventional bomb blasts ranging from 1 to 20 kg of TNT confirmed that proximity to explosion is more important to the size of the charge. At distances greater than 6 meters victims will probably not have mortal wounds. A SCUD missile explosion in military personnel housing injured the ears of 172 individuals. Of the 86 hospitalized, 76% had ear drum perforations. Distances to explosion were measured and used to construct mathematical model of estimated wave form. Fifty percent of soldiers will sustain a ear drum perforation at 185 dB (15 PSI).
Middle ear damage, such as Tympanic membrane perforation is always an indication of cochlear damage. An important point requires consideration. Tympanic membranes can be surgically repaired. However, there are no medical/surgical procedures to repair cochlear damage.
As in military applications, protection to the hearing organ is important in occupational and industrial settings. Impact noise in the industrial sector presents a problem similar to blast overpressure in the military sector. According to the U.S. Department of Labor, 28.4 per 10,000 workers will have recordable hearing loss (2004) US Dept Labor. Ten million have experienced permanent hearing loss, 30 million are exposed to dangerous noise levels daily (NIOSH)
Industrial Devices such as electronic ear muffs amplify outside noise so those with impaired hearing can hear warning bells. The problem is that they transmit noise and directed communication with equal intensity making no distinction between the two. Although they do not electronically transmit noise over a set dB range (often set to >85 dB), they are unable to intercept harmful sound energy which continue onto the middle and inner ear unabated.
A decibel is a sound pressure level. A whisper is 20-30 dB, normal speech is approximately 50-60 dB. A jet engine at 30 meters is 150 dB. A loud factory is 90 dB. A pneumatic hammer at 2 meters is 100 dB. The Krakatoa explosion at 100 miles was 180 dB. A rifle being fired is 140 dB. OSHA defines dangerous hearing loss at greater than 85 dB over a normal 40 hour work week. The standards in other parts of the world are more stringent.
The Israeli medical association reported that 33 out of 34 of people who survived a suicide terrorist attack on a municipal bus sustained hearing damage, yet all patients had normal electronystagmography indicating vestibular function remained unaffected even in close proximity to the blast. i.e. the bony encasement of the semicircular canals protected them against the blast overpressure force while the more vulnerable hearing organs were uniformly damaged.
In past, various attempts have been made to provide earplug or ear protectors. Such past attempts include U.S. Pat. No. 4,807,612 entitled “Passive Ear Protector,” U.S. Pat. No. 4,852,683 to “Earplug with Improved Audibility,” U.S. Pat. No. 5,113,967 entitled “Audibility Earplug,” U.S. Pat. No. 6,070,693 entitled “Hearing Protector Against Loud Noise,” and U.S. Pat. No. 6,148,821 entitled “Selective Nonlinear Attenuating Earplug.” While these past attempts may have provided some attenuation of or protection against loud noises, they did not provide the protection provided by the present invention in combination with not substantially limiting or adversely affecting normal hearing.